Universe Expansion

You appear to be claiming that the movement of the Local Group is evidence against cosmic expansion, in spite of having had it pointed out to you that the distances between members of the Local Group are too small for cosmic expansion to be expected to dominate over motion due to gravitation.

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You are not being honest. Read again what I said..

RajeshTrivedi said:

When we cannot observe any expansion at such small distance (2.5 mly is small for metric expansion), then the question of overcoming does not arise. Yes, it fits with our argument, that gravity is pulling them at a faster rate, absence of expansion in local clusters is not a very inconvenient observation for current models.

So the relative movement through space of the 2 galaxies if there was no expansion would be 600,000 km/hr

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Appreciated.
I will recap, the point, which is more or less quite popular, is that for nearby galaxies the cosmological expansion is overcome by gravity. This was being copy pasted or reiterated by NotEinstein couple of times, so I asked him to point out some scientific article with maths, which could establish it.

I also acknowledged that this overcome by gravity aspect appears quite plausible and prima facie non problematic to current models, but lacks maths. Exchemist naively linked back some popular article and NotEintein continued with word games.

You attempted some maths, great, but there is a problem in your argument, it does not conclude or establish that gravity overcomes metric expansion.

Lets see..

1.

1. We calculate the possible closing in speed due to gravity, say A.
2. Then we calculate the possible expansion speed due to Hubble, say B.
3. So the actual observed speed of Andromeda should be C = A-B

You have calculated B (that is 203000 km/hr, fine), and you have used observed closing in speed C (that is 400,000 km/Hr), to arrive at A = 600,000 km/Hr. Thats bad reasoning idealy should get C from A and B thus conclusively nailing it.

At what distance is the closing speed through space equal to the expansion of space:

\(\frac{600,000 km/hr}{ 260,000 km/hr/Mpc} = 2.3 Mpc\)

So simply looking at the current closing speed of the Andromeda galaxy, if the galaxy was 'magically' moved to > 2.3 Mpc from the Milky way galaxy, then they would be receding from each other. The actual velocity through space of the galaxy would be less than the expansion of space between the galaxies.

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This is problematic. What you are implying that for Andromeda-Milky way mass with 2.3 Mpc at distance (Not Eisntein, read this carefully, you failed to understand the need of strategically massed and spaced earlier on) the relative speed between two will be nil and beyond that "only redshifts". There are no such observations, in fact there are around 7000 recorded galaxies with blue shift, many of them are at > 2.3 mpc and less bulkier (lesser gravitational effect still blue shifted).

The biggest conceptual issue which cannot be sidestepped for argument is: Hubble constant (260,000 km/hr/Mpc) is not so certain for such small distances. Hubble applicability is quite reliable if we talk of d > 1 bly, something more than 100 times the distance between Andromeda/MW. Face it, we have absolutely no observation of expansion at such cosmological small distance (2.3 Mpc).

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I will recap, the point, which is more or less quite popular, is that for nearby galaxies the cosmological expansion is overcome by gravity. This was being copy pasted or reiterated by NotEinstein couple of times, so I asked him to point out some scientific article with maths, which could establish it.

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Not an entirely faithful representation of our past discussion. You outright rejected the idea, and then demanded I provide proof for my position while you were unable/unwilling to provide any for yours.

(Not Eisntein, read this carefully, you failed to understand the need of strategically massed and spaced earlier on)

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Oh yeah, thanks for reminding me about that. You threw out these terms, and then ignored me when I asked you for clarification about what you meant. I guess you can count that as another instance of your own "word games". And don't forget the intellectually dishonest tactic of refusing to explain your (as far as I can tell) non-standard terminology and then blaming the other party for "failure to understand". I think I have figured out why other people have been calling you a troll.​

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Not an entirely faithful representation of our past discussion. You outright rejected the idea, and then demanded I provide proof for my position while you were unable/unwilling to provide any for yours.

So you agree with me that it is you who is going against current models, and thus carry the burden of proof. Great!

Excuse me, but you are the one that has been moving goalposts, and refusing to provide evidence for their claims. If anybody has been playing word games in this discussion, it's you.

Edit:

Oh yeah, thanks for reminding me about that. You threw out these terms, and then ignored me when I asked you for clarification about what you meant. I guess you can count that as another instance of your own "word games". And don't forget the intellectually dishonest tactic of refusing to explain your (as far as I can tell) non-standard terminology and then blaming the other party for "failure to understand". I think I have figured out why other people have been calling you a troll.​

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You have ranted (#218) enough on this thread, still I will give you one more chance.

You have been reiterating that expansion between Andromeda & Milky Way is present but overcome by gravity.
I am saying that there is no observational evidence of any such expansion, however this lack of observation is not detrimental to current models, but it lacks robust maths.

Origin has attempted some maths, you lazily but pompously agreed with him, I have given rebuttal to that. See if you can handle that. No more word games pl.

however this lack of observation is not detrimental to current models, but it lacks robust maths.

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Alright, since you seen to be unable to locate the maths yourself, let me help you out. It's a natural consequence of the FRW metric. So please point out how it is possible for the Hubble parameter to be locally zero, but not globally, when there's no position-dependence in its definition:https://en.wikipedia.org/wiki/Scale_factor_(cosmology)#Detail

Why are you asking me to fight somebody else's battles? Let us focus on ours: you still haven't provided any reason to doubt the current models; I'm still waiting for you to provide any evidence for your claims.

Alright, since you seen to be unable to locate the maths yourself, let me help you out. It's a natural consequence of the FRW metric. So please point out how it is possible for the Hubble parameter to be locally zero, but not globally, when there's no position-dependence in its definition:https://en.wikipedia.org/wiki/Scale_factor_(cosmology)#Detail

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Another boastful arrogant attempt. But it shows your complete lack of understanding at conceptual level. FLRW metric has a primary assumption of homogeneity and isotropy, which is applicable at large scale cosmological distances > 250 mly. We are discussing 2.5 mly only.

So as of now your position is "observationless" and "mathsless". You are blindly following what authority says.

So that makes your argument more or less "faith in authority" based on random reading of popular articles.

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It's not so much an argument, as a statement about what the currently accepted models (that have been tried and tested) state. And please provide evidence that my "argument" is based on random reading of popular articles.

But it shows your complete lack of understanding at conceptual level. FLRW metric has a primary assumption of homogeneity and isotropy, which is applicable at large scale cosmological distances > 250 mly. We are discussing 2.5 mly only.

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Sure, but please explain to me how space can expand over stretches of >250 mly, if it does not expand over stretches of 2.5 mly.

Have you already forgotten the maths provided by Origin?
Only if your rebuttal remains standing; so let's wait until Origin responds before making that judgement.

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No, I dont forget so easily. When origin posted that maths, you tried to show off that you could have given, but for your laziness. That means you primarily agreed with his maths. Give the rebuttal, if you can.

That means you primarily agreed with his maths. Give the rebuttal, if you can.

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Why should I? You have many, many times failed to provide even the slightest amount of evidence (or maths) for your claims; what gives you the right to demand I do when you are unwilling or unable to the same? (I'm getting flashbacks to your own usage of the word "pompous"!)

And you haven't proven that this thus means there is no expansion at smaller scales.

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But you agreed that there is no observation of expansion between Andromeda and MW. There is no need for me to prove anything on this.
And your hinting of FLRW metric also falls flat, as this metric applicability at 2.5 mly type scales is in contrast with its primary assumption.

I believe in the current models and what they predict until evidence is shown that they are wrong. So for the umpteen time + 1: please provide evidence the current models are incorrect.

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Thats visible that you believe in current models.
What is clear from this is that you believe blindly;
You agree that there is no evidence of expansion, you have no maths, neither you have provided nor you have attempted and nor you have attempted to rebut my counter to Origin's attempt. So that makes it very clear that you have no maths to offer or cite. You are more into belief, like a theist.

That laziness wasn't limited to merely writing it down; there's also a bit of understanding involved. (Not understanding of what the current models says, but of why it says it.)

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Oh!
See, in another thread on Special Relativity, how you and Exchemist tried to put down and adhom Zeno, untill Janus, without naming you guys, indirectly, taught you how to rebut mistaken claims.

Sorry guys, both of you have no constructive contribution here, except shouting time and again that you are with the current models. That is more out of inability to think critically, more out of belief in authority not out of any indepth understanding of the topic in hand.

And your hinting of FLRW metric also falls flat, as this metric applicability at 2.5 mly type scales is in contrast with its primary assumption.

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Please provide evidence or maths for this claim. Assuming that the universe is homogeneous (etc.) at large scales doesn't preclude the possibility that the FLRW metric is also (locally?) valid on smaller scales.

Thats visible that you believe in current models.
What is clear from this is that you believe blindly;

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False. I've read about the evidence backing it up. Ever heard of the big bang theory, or modern cosmology in general? Seems to me there's quite a bit of evidence suggesting the current models are quite good. That you blindly disbelieve established science says more about you than the science.

untill Janus, without naming you guys, indirectly, taught you how to rebut mistaken claims.

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What's your point? Are you so pompous as to demand I am not allowed to be as lazy as you are? Are you really so pompous as to demand I invest time to understand all the ins-and-outs of something just to counter your baseless assertions? Why don't you take a page from Janus' book, and actually provide the evidence and maths behind your claim. Are you really so horribly pompous that you don't see that what you are complaining about fits you better than me?

Please provide evidence or maths for this claim. Assuming that the universe is homogeneous (etc.) at large scales doesn't preclude the possibility that the FLRW metric is also (locally?) valid on smaller scales.

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If there is an assumption of homogeneity and isotropy for working out FLRW metric then it is very natural that it wont be valid if the assumption fails. This is the basic aspect of working on maths or science. Why are you having trouble understanding this? Why are you making such naive statements that since it is applicable at larger scales, nothing precludes its validity for smaller scales. If so extend your fallacious argument till quantum level!!

If there is an assumption of homogeneity and isotropy for working out FLRW metric then it is very natural that it wont be valid if the assumption fails.

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But not necessarily true. Also, perturbations of the homogeneity and isotropy are allowed. The question you need to answer is whether in the given scenario the deviations from the ideal are large enough to invalidate the metric.

Why are you making such naive statements that since it is applicable at larger scales, nothing precludes its validity for smaller scales.

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Because that's true? Take a fully homogeneity and isotropy universe: the metric is now also valid on smaller scales. You need to prove that the given scenario deviates enough for the metric to fail at these scales.

The first link we obviously both agree with, so I'm not sure why you bring it up.

The second link: this doesn't support your position, as I've just explained above. Also, you haven't posted any maths. Remember you continuously waving away arguments because there was no math? Additionally, funny how you are talking about "basic aspect(s) of working on maths or science" and you have missed the basic aspect of providing any yourself.

Moderator note: RajeshTrivedi has been permanently banned from sciforums. Previously, this user was directly queried about whether he was a sock puppet of a previously-banned user. He lied directly to me in response to that query.

Moreover, this user continually demands evidence from others while posting none of his own. This is classic troll behaviour, and it is a waste of everybody's time.

Moderator note: RajeshTrivedi has been permanently banned from sciforums. Previously, this user was directly queried about whether he was a sock puppet of a previously-banned user. He lied directly to me in response to that query.

Moreover, this user continually demands evidence from others while posting none of his own. This is classic troll behaviour, and it is a waste of everybody's time.